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Home , Algodonite, Cuprite, Digenite, Domeykite, Native copper, Tenorite

are generally anhedral, euhedral crystals and crystal aggregates of occur relatively commonly in COPPER vugs. Cu Composition: Arsenic occurs in small amounts in is easily the most famous of all of ’s native copper deposits. Some of Michigan’s . As an , native it occurs as copper arsenides (, copper is very rare throughout the world, although ), but the bulk of it is present in solid minor occurrences are widespread. The greatest solution with the copper. The arsenic content native copper deposits ever found and exploited varies from a few ten thousandths of a percent to are those of the in over half a percent - a thousand-fold variation. Michigan’s Northern Peninsula. Copper mineral- Broderick (1929) has shown that in most mines the ization occurs along a narrow belt over 150 As:Cu ratio increases with depth and, in general, kilometers long, stretching southwestward through the higher the ratio the greater its rate of increase. Keweenaw, Houghton, and Ontonagon Counties (Part I). There, native copper occurs in Alteration: Copper from many of the mines is amygdaloids, conglomerates, and fissures ranging coated by a of reddish or black in size from microscopic grains up to masses 14 , which, in some instances, may have meters long and weighing 382 metric tons formed after the mines were opened. However, in (Rickard, 1905). Similarly large masses of float some deposits, particularly in higher levels, the copper have been found in glacial drift, particularly in the Northern Peninsula. (Rickard, 1905; Kraus, 1924), though native copper erratics are known in glacial drift in Wisconsin, Iowa, Illinois (Crook, 1929), Indiana, Ohio, Western New York, and Pennsylvania. While these large masses of copper

Figure 61: Native copper, wire copper with datolite from the Osceola mine, Calumet, Houghton County, field of view 7 cm, A. E. Seaman Mineral Museum specimen No. JTR 1671, Jeffrey Scovil photograph.

oxidation was pre- in origin (Butler and Burbank, 1929). forms similar coatings. Pseudomorphs of cuprite (q.v.) after copper are also known. Habits: The aggregate forms assumed by copper are highly variable, and a number of distinctive types have been recognized: Figure 60: Native copper with cuprite (red) and tenorite 1. Grains, blebs, pellets, and masses. Anhedral (black) patina from the Central mine, Central, Keweenaw to subhedral. County. 4.5 x 12 cm. A. E. Seaman Mineral Museum specimen No. JTR 537, Jeffrey Scovil photograph. 2. Masses. The larger pieces commonly are very irregular with a hackly appearance. 3. Crystals and crystal groups. 4. Networks. Interconnecting irregular veinlets, Crystallography: The crystallography of Michigan sheets, plates, and aggregates. native copper was studied in detail by Dana (1886), 5. Thin sheets. Formed in narrow fissures or who identified the following forms: planes. An unusually fine specimen Cube {001} of sheet copper is in the University of Dodecahedron {011} Michigan collection. It measures 1.5 meters long, 0.3 to 0.6 meters wide, and about 5 mm Octahedron {111} thick and shows parallel striations. Tetrahexahedrons {014},{025}, 6. Filiform or “wire.” {012}, {035}

7. Arborescent. Three-dimensional fernlike Trapezohedrons {113}, {112} groups. Some variants are also described as Hexoctahedrons {51018}, “moss copper.” An unusually fine and large {1611},{2312} specimen in the University of Michigan collection is a reticulated aggregate of distorted, elongate, semi-flattened crystals The most common habit is tetrahexahedral, with over a meter long, 15 to 30 cm wide, and 5 {014} and {025} the most common forms. These to8 cm thick. may be combined with the cube, dodecahedron, or 8. Leaf. Dendritic aggregates flattened in one (rarely) octahedron. The cube alone is also plane. relatively common, the dodecahedron less common, and the octahedral form alone much less 9. Brick. Massive, replacing sandstone. common. Wilson and Dyl (1992) showed that 10. Shell. Molds of boulders and cobbles. Also may be related to crystal size. In a called “skull copper.” An outstanding preliminary study “of copper crystals 4 mm or less specimen is shown by Kemp (1980, page in diameter, in close association with prehnite and 260). It measures 17.5 x 11.5 x 14 cm, and is commonly also with quartz and calcite..nearly 70% from the Calumet and Hecla mine, Houghton of the copper crystals with identifiable forms County. proved to be the tetrahexahedron {057}, and half 11. Shot. Vesicle fillings. the remainder are this form modified to some 12. Spike. Elongated vesicle fillings. An extent by the dodecahedron.” Larger crystals were extraordinary spike is in the University of found to have a higher proportion of other Michigan collection. Set in an altered basalt tetrahexahedron forms, along with the cube, base, it is approximately a meter long and 5 to octahedron, and dodecahedron. Figures 60 to 66 15 cm in diameter, tapering upward, with a illustrate some of these forms. “flopped-over” point. 13. Pseudomorphs. Replacements of feldspar, calcite, or boulders. 14. Half-breeds. Intergrown masses of copper and silver. 15. Barrel. “Ponderous hackly masses” (Rominger, 1895).

Figure 62: Native copper, a rare, 2 cm, hexoctahedral copper crystal from the Osceola mine, Calumet, Houghton County, A. E. Seaman Mineral Museum specimen No. JTR 1672, Jeffrey Scovil photograph. Distortions are widespread, giving rise to crystals with marked pseudosymmetry. Preferential elongation along a single crystal axis yields pseudotetragonal crystals. Examples of rhombohedral pseudosymmetry are also common. Some crystals may be skeletal, cavernous, or hollow. In some, the edges of the crystals project above deeply depressed faces. Also common are striations, pits, growth projections, and wavy surfaces. Twinning on {111} is very common, giving rise to simple contact twins, a few penetration types, and less commonly repeated twinning (Dana, 1886). X-ray powder diffraction data for copper (Calumet and Hecla mine) and for arsenian copper (Houghton County) are given by Berry and Thompson (1962, page 12).

Baraga County: Huron Islands: Dana (1892) Figure 64: Native copper, dendritic growth of cubic reports “native copper in granite.” Unconfirmed. crystals from the Calumet and Hecla mine, Calumet, Dickinson County: 1. Cyclops mine at Houghton County, 5.5 x 8.5 cm, A. E. Seaman Norway: Float copper in drift above the iron ore Mineral Museum specimen No. JTR 674, Jeffrey Scovil body. 2. Reportedly the largest mass of float photograph. copper found in Dickinson County was uncovered in the early 1940s during excavation for a filling

Figure 63: Native copper, “Fern” copper from the Phoenix mine, Phoenix, Keweenaw County, 4.5 x 5.5 cm, A. E. Seaman Mineral Museum specimen No. JTR Figure 65: Native copper, parallel growth of cubic 1664, Jeffrey Scovil photograph. crystals, copper district, 2.5 x 7.5 cm, A. E. Seaman Mineral Museum specimen No. GBR 569, Jeffrey Scovil photograph. northwest of Franklin mine: A large piece of float copper, showing glacial striations and evidence of partial working by Native Americans, weighing 220 kg and measuring 80x 105x 15 cm is now in the Mineralogical Collection of the University of Michigan (Kraus, 1924). 6. Hancock mine: Very good crystals. 7. Isle Royale mine: In lodes and feeding fissures (Broderick, 1931) and disseminated in epidote. 8. Kearsarge mine: Fine crystals in lodes and fissures, sometimes associated with silver (Broderick, 1931). 9. Osceola mine: Very fine crystals, wire (Number 13 shaft), and sheet copper. Wire copper in an intertwined cluster 10 cm high (specimen JTR 1670) is in the A. E. Seaman Mineral Museum (MacFall, 1983). Vugs with perfect small crystals. The famous sheets occurred in fissures in the diabase on the hangingwall of the Osceola amygdaloid (Rominger,

1895). 10. Quincy mine: Fine crystals, many with Figure 66: Native copper, twinned tetrahexahedrons from dodecahedral habit, and microcrystals in the Central mine, Central, Keweenaw County, 6 x 8 cm, amygdules. 11. Tamarack mine: Sheet copper, A. E. Seaman Mineral Museum specimen No. DCG shell copper (boulder casings), and pseudomorphs 1110, Jeffrey Scovil photograph. after calcite. 12. Winona mine: Fine crystals. 13. Wolverine mine: Excellent crystals, reticulated station in Iron Mountain. It is estimated to have masses, and shot copper. 14. Hancock: Ancient been about a meter across, 1 - 2 cm thick, and mine pits were uncovered in the south parts of “only slightly oxidized” (B. J. Westman, written sections 25, 26, and 27, T55N, R34W (Hinsdale, communication, 1983). 1931). 15. Champion mine: Arborescent crystal Gratiot County: Near Ithaca, T10N, R2W in groups. 16. Six Mile Hill, east slope; southwest of Michigan Basin Deep Drill Hole in the altered Houghton: Copper, calcite, and epidote in a upper basaltic-gabbroic unit. An accessory with network of veins. Copper in masses of 1 to 40 and digenite in albite-chlorite-calcite- kilograms. Seams also contained considerable epidote rock (McCallister et al., 1978). and some prehnite and datolite (Rominger, 1895). 17. Pewabic mine: As well- Houghton County: 1. Atlantic mine: Large formed crystals and pseudomorphs of copper after masses. A large calcite vein transected the laumontite and after quartz (Pumpelly, 1873). 18. amygdaloid at which junction it contained nests Other mines that have yielded fine specimens and pockets of copper and silver (Rominger, include: Arcadian, Franklin, Laurium, and 1895). 2. Baltic mine: Fine crystals in lodes and Trimountain. “feeding fissures” (Broderick, 1931) with chalcocite. Groups of elongated, reticulated Iron County: 1. Bengal (Cannon) iron mine: crystals. A fine group (specimen JTR 550), 19 cm Thin post-ore foils in iron ore (James et al., 1968); across, is in the A. E. Seaman Mineral Museum also with schorl (T. M. Bee, personal communi- (MacFall, 1983). 3. Calumet and Hecla mine: Many cation, 1999). With manganese minerals in the varieties, including boulder cases, replacements of oxidized zone of Young’s iron ore body in the boulders, pseudomorphs after feldspar including Riverton Formation (Kustra, 1961; Brower, 1968). one after a feldspar crystal 5 cm long (Harvard Spectacular leaf copper in veinlets in several University collection, #85739), and “shot copper.” stopes. 2. Great Western mine, 10th level, Crystal Also “skulls” around rhyolite cobbles. 4. Falls: Similar occurrence in sheared hematite and a Centennial mine: Brick copper replacing sandstone, magnesium-rich neotocite-like mineral (A. E. fine microcrystals, excellent large crystals, “skulls”, Seaman Mineral Museum, specimen DM 1890). and leaf copper. 5. John Gaspardo farm, 4 km Keweenaw County: 1. Ahmeek mine: Fine inclusions of copper in agate from Isle Royale crystals and groups including copper inclusion beaches. 10. Stromatolite limestone beds in the phantoms in calcite crystals. 2. Central mine: Fine Copper Harbor Conglomerate in the vicinity of crystals in vugs and shot copper. Also masses, Copper Harbor: Microscopic native copper has some many tons in weight (Rominger, 1895). been found in stromatolites near Dan’s Point, Groups of fine dodecahedral crystals. One Horseshoe Harbor, and 1 km east of Horseshoe specimen (JTR 526), 10 cm across, is in the Harbor, where the Copper Harbor Conglomerate A. E. Seaman Mineral Museum (MacFall, 1983). is cross cut by the “Lakeshore veins,” which 3. Cliff mine: Superb crystals. Whitney (1859) notes contain laumontite, chalcocite, barite, chlorite, this locality as producing the finest quality single calcite, and fluorite. The copper occurs in vugs in crystals. They were mainly of tetrahexahedral the stromatolites and associated oolite-oncolite habit. Many were twinned. Microcrystals from the beds (Nishioka et al., 1984). 11. Eagle Harbor: In Cliff far surpass all others. Single crystals occur as 1971 Don Pearce of Calumet collected many complex cubes, tetrahexahedrons, octahedrons, or hundred kilograms of well-crystallized copper from dodecahedrons. The copper is closely associated an underwater vein in Lake Superior near Eagle with prehnite. Wire copper, moss copper, and Harbor, known locally as “Grand Marais,” or arborescent masses are also found. Williams “Gull Rock.” The herringbone to arborescent (1966) reports good crystals “abundant everywhere crystal groups were enclosed in calcite. One along the vein.” The majority is dominated by specimen weighing about 45 kg consists of a face {124}, modified by {001}, {011}, and {111}. half a meter across of fine herringbone copper Many distorted crystals are triangular plates on with large blocky crystals on the opposite side {111}, bounded by various hexoctahedra. 4. (Wilson, 1983b). 12. Point prospect: Some of the Copper Falls mine: Whitney (1859) states (page 11), world’s largest crystals of native copper came from “no other (locality) has furnished any specimens to a small fissure vein exposed during road compare with those found here.” Many of the construction approximately 10 km southeast of superb crystals range in size from a few millimeters Copper Harbor, known locally as “Point to about 2.5 cm. The dodecahedron is the prospect.” The crystals have an overall predominant form in groups of crystals, but the dodecahedral aspect, often in combination with an octahedron is also found. A large 73 metric ton unidentified tetrahexahedron form. Crystals up to mass of copper came from this mine. Some spike 6.4 kg are known (Rosemeyer and Carlson, 2000). copper is found. 5. Mohawk mine: High-arsenic 13. Other mines that produced native copper in copper (Stoiber and Davidson, 1959). 6. Phoenix excellent specimens include: Allouez, Clark mine: Excellent crystals, leaf copper, moss copper (Copper Harbor), Delaware, Iroquois, Kingston, with analcime, and arborescent groups. 7. Seneca Medora, Northwestern, Ojibway, and Star. Also mine: Fine microcrystals in amygdules (Moore and found at Five and Seven Mile Points at Eagle River Beger, 1963) plus arsenian copper (Stoiber and and at Hays Point at Copper Harbor. Davidson, 1959). 8. Drill hole Delaware 77, Dead River: In quartz- T58N, R30W: Disseminated in unaltered layers in a Marquette County: 1. carbonate- veins (Puffet, 1966). Also in flow above the Kearsarge Conglomerate (Cornwall, small seams in quartz at the Fire Centre gold mine, 1951a). Isle Royale: Prospectors reaching the 9. section 35, T49N, R27W (M. P. Basal, personal island in the late 1840s found that all the major communication, 1999). 2. Eastern Marquette iron copper lodes on the island gave evidence of range, NE ¼ NW ¼ section 1, T47N, R25W: In prehistoric mining in the form of pits as much as 9 fractures and interstitial grains replacing quartz meters across and as deep as 18 meters. Rock- grain boundaries in red quartzite (Reed, 1967a, b). copper masses as heavy as 2,700 kg were found to have been raised by cribwork. The excavating and Ontonagon County: 1. Adventure mine: Fine mining were accomplished by means of crystals. 2. Minesota mine: Crystals, leaf copper, and hammerstones or mauls along with fracturing of large masses. 3. Victoria mine: Fine crystals. 4. the rock by fire-heating and quenching with water White Pine mine: In the Nonesuch Shale as (Drier and DuTemple, 1961). A completely disseminated grains and as thin sheets along different occurrence of native copper has been fractures in the lower part of the ore zone noted by Sukow (1987, 1990), who described associated with chalcocite and native silver, the latter commonly forming rims on the copper (Doane, 1956; Carpenter, 1963; Brown, 1966, UPDATE 1968; Rosemeyer, 1999). It also occurs disseminated and in veinlets in the chloritic facies Alger County: Approximately 7 kilometers east of the Copper Harbor Conglomerate (Hamilton, of Grand Marais: As microscopic flakes with gold 1967). 5. Ontonagon Boulder: This float boulder and rare platinum (q.v.) in black sands in sand of native copper, (Figure 3) destined to become dunes (M. J. Elder, personal communication, famous in American history and also in the annals 2006). Verified by energy dispersion X-ray of the (“The Great Copper spectrometry. Rock”), was found half buried in the muddy bank of the west branch of the Ontonagon River. The Huron River uran-ium Reportedly, French explorers had hacked off Baraga County: prospect, NW ¼ NW ¼ section 1, T51N, R30W: souvenir pieces as early as 1664. Alexander Henry, As rare thin sheets and dendritic growths along who visited the area in 1760, examined it in the fracture surfaces with cuprite (Carlson et al., side of the stream bed about 32 kilometers above 2007a). the mouth of the river and chopped off a 45- kilogram portion with an axe. The locality is given as that now occupied by the Victoria Dam, which Houghton County: 1. Houghton: Cubic crystals is in section 31, T50N, R39W. Details on the of native copper have been found in a calcite vein legendary peregrinations of the Ontonagon exposed in a small traprock quarry operated by Boulder are presented by Pantell (1976). 6. Moyle Construction Company. 2. Copper occurs Another famous float boulder of copper found as bands in agate amygdules at the Wolverine No. near the mouth of the Ontonagon River was 2 mine, Kearsarge, the Calumet & Hecla No. 21 described by Catlin (1835) as weighing 62 shaft in Calumet and the Saint Louis mine in kilograms and showing “rudiments of crystals with Laurium. The amygdules vary in size from 1-10 cm triangular faces” as well as incrustations of a “green (though most are ~ 2-3 cm), and from gray to carbonate of copper.” The copper boulder was beige or pink in color, with small agate “eyes” donated by Mr. Catlin to Yale University. 7. developed along their outer edges. Paragenetically, Numerous prehistoric excavations for copper, the agate appears to have preceded the copper, including a shaft 7.5 meters deep, were found from which in turn appears to have selectively replaced Mass City to Victoria, and halfway between certain bands in the agate (Rosemeyer, 2012). Victoria and Bergland (Hinsdale, 1931). 8. Though small, these unique agates are quite Porcupine Mountains: Veinlets of calcite, quartz, attractive, and are popular with both lapidaries and epidote, and traces of native copper. 9. Ridge mineral collectors. mine: Pseudomorphs after quartz crystals. 10. UPDATE FROM: Robinson, G.W., and Bohemian mine: A magnificent distorted Carlson, S.M., 2013, of Michigan tetrahexahedral crystal 1 cm across (MacFall, 1983, Update: published online by A.E. Seaman Figure 66). 11. Other mines well known for fine Mineral Museum, Houghton, MI, 46p. specimens during their periods of activity are Algomah, Caledonia, Indiana, Lake, Mass, Michigan, Morris, and National. Tuscola County: Southern Tuscola County; a float mass weighing 29 kilograms was plowed up and placed on exhibit in a Mayville hotel for many years. FROM: Robinson, G.W., 2004 Mineralogy of Michigan by E.W. Heinrich updated and revised: published by A.E. Seaman Mineral Museum, Houghton, MI, 252p.

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Copper replacing bands of agate in a 3-cm amygdule from the Wolverine No. 2 mine, Houghton County. A. E. A 7 cm branching aggregate of cubic copper crystals from the Seaman Mineral Museum specimen DM 30339, George Moyle Construction Quarry in Houghton, Houghton Robinson photograph. County; A. E. Seaman Mineral Museum specimen DM 28332, George Robinson photograph.